This invention is in the field of optical particle analyzers. This invention relates generally to two-dimensional optical imaging-based methods and systems for detecting and characterizing particles in fluid samples. This invention also relates generally to methods and systems for improving the sensitivity and versatility of optical particle analyzers and for extending device performance of these systems so as to accurately detect and characterize particles having small physical dimensions (e.g., less than 0.1 microns).
A large portion of the micro-contamination industry and clean manufacturing industries is reliant on the use of optical particle counters, such as are described in a large number of U.S. patents, including U.S. Pat. Nos. 3,851,169, 4,348,111, 4,957,363, 5,085,500, 5,121,988, 5,467,188, 5,642,193, 5,864,399, 5,920,388, 5,946,092, and 7,053,783. Particle counters are also described in U.S. Pat. Nos. 4,728,190, 6,859,277, and 7,030,980, 5,282,151, which are hereby incorporated by reference in their entirety.
Optical particle sensors and counters are useful in a variety of industrial applications including in semiconductor, pharmaceutical and microelectronics industries. In some industrial settings, optical particle sensors and counters provide an important tool for continuously monitoring the composition and purity of materials used in a process, for example, in the production of pharmaceutical products subject to stringent regulatory requirements relating to particulate contaminates. In other industrial settings, optical particle sensors and counters provide an important tool for providing quality control analysis, for example for off-line quality control checking of high quality photoresist and semiconductor materials. It is particularly advantageous to rapidly identify when a fluid is contaminated with unwanted particles so that the process can be stopped at an early stage, thereby avoiding wasteful manufacture of defective product. For example, in semi-conductor and other clean-room settings, or industries requiring sterile and pure production (e.g., pharmaceuticals), material fluids that are used to make the end products are continuously monitored to ensure adequate purity and that any unwanted particles suspended in the fluid is within an acceptable tolerance range. Aerosol particle counters are often used to measure air-born particle contamination in clean-rooms and clean zones. Liquid phase particle counters are often used to measure particulate contamination in pharmaceutical, water treatment and chemical processing industries.
The importance of particle monitoring sensors is reflected in the continuous and ongoing improvement and development of these devices to improve reliability and throughput, and to enable detection and characterization of particles having smaller sizes. In addition to limitations on sensitivity and particle sizing capability, state of the art optical particle counters are currently susceptible to problems relating to false counts generated when detector noise and/or signals resulting from processes other than optical scattering from particles are attributed to a particle detection event. The occurrence of false counts adversely impacts accuracy and sensitivity of the systems. Furthermore, the occurrence of false counts also impedes the capability of optical particle analyzers to accurately detect and characterize particles having small physical dimensions (e.g., less than 0.1 microns). As a result, design strategies for avoiding or suppressing false counts in optical particle counters and analyzers is recognized as a priority in development of the next generation of these devices.